Plastic base



FIG. 1 is a perspective view of the plastic base;

FIG. 2 is a top plan view;

FIG. 3 is a front side view, the rear side being the mirror imagethereof;

FIG. 4 is a right side view, the left side view being the mirror imagethereof; and,

FIG. 5 is a bottom plan view.

The ornamental design for a plastic base, as shown and described.